Switches of the afore-mentioned type, on the one hand, should be able to switch substantial load currents so as to pass energy to lamps and engines. On the other hand, switches of the afore-described type increasingly serve for indirectly actuating power consuming units then actuated directly through electronic circuits. Advantageously, steering column switches of this type should, therefore, also be able to switch weak control currents.
In order to be able to neatly switch also weak flows of this type, the transition resistance of the switches is to be kept low. Special provision is, therefore, to be made to prevent pollution of the communicating contact faces by corrosion, scaling, arc formation or adhering residual insulating material.
In conventional switches, contact sections rigidly arranged on the housing in abutting relationship within the contact plane are electrically interconnected or separated by a pushing motion of contact bridges. The disadvantage involved with switches of this type resides in that the two contact sections are separated by insulating material that will get into close contact with the contact bridge when sweeping about it. The displaced contact bridge will thereby entrain remainders of insulating material or of the plastic casing in which are embedded the contact sections. Once the contact bridge runs up another contact section, the insulating material, in part, is transferred to the contact bank of the said contact section or is burnt into the contact faces by the arc, if formed, thereby polluting the contact face. By sizing the switch adequately large, the bearing force of the contacts can so be dimensioned that during the counter-directed pushing motion the contacts are again rubbed clean. However, large-dimensioned switch sizes are not justifiable for weak currents.
It is the object of the invention to provide a small-sized switch, the contact faces of which are substantially kept free from pollution so as to enable use thereof as a switch for large and weak currents. Hence, the invention resides in that the contact bridge is raised at an appropriate point before leaving a contact section to be then lowered at an appropriate point of a new contact section.
Accordingly, the pushing motion, at the important re-switching points, is combined with a lifting motion. The resultant advantage resides in that the actual contact face is not placed in contact with the insulating material surrounding the contact sections. Moreover, contact making, due to the lifting motion, is abruptly changed rather than linearly by a dragging movement through passage from one contact section to the next. Hence, three defined conditions of the contact bridge are attained in respect of which the transitory times are relatively short, to wit: contact making of the contact bridge in one contact section only; contact making of the bridge to one bridge portion only with the other bridge portion lifted off; and, finally, rapid transition to the condition connecting the two contact portions respectively to another contact section. Also, it is of importance to the invention that one of the contact portions, during lifting, does not yet form an arc because the other contact portion is still in close electrical contact with the contact section.
A particularly simple design suitable for lifting off a contact portion is disclosed according to which a ramp is provided over which a contact portion of the contact bridge moving along a contact section is raised in a direction vertical to the plane of the contacts and lowered over the next contact section. Hence the motion of the contact portion follows the oblique sloping ramp faces.
To reliably prevent areas of the contact bridge dragging along the stationary contact sections from getting into contact with the surrounding insulating material, in particular, with the insulating material of the ramp, at least one ramp is provided which is arranged laterally of the contact faces of contact bridge and contact section so that the area of the contact bridge running on the ramp will not get into contact with the contact face on the contact sections.
To that extent, a particularly simple design is set out wherein the ramps are symmetrically arranged within the interval so that the forces exerted by the two ramps on the contacts are also symmetrical, thereby keeping the contact bridge well in trace with the contact sections. To reliably separate the portions of the contact bridge in communication with the ramp or insulting material, if any, from the portions serving to establish contact with the contact sections, the contact zones previously referred to as contact portions are formed on the contact bridge that get into electrical contact with the ramps but not with the contact sections. Moreover, contact zones are formed that exclusively get into contact with the contact sections to establish a reliable electrical contact.
To improve contact making between contact bridge and contact section, a preferred embodiment is disclosed for conducting weak currents as due to the dragging motion of contacting faces that, conversely, never get into contact with plastic material and are easily separated with no major arc formation, the contact faces can be kept substantially clean. Usually, no special coating is required.
For further reducing the contact face to facilitate cleaning of the contacts, contacts can be constructed having a pointed bearing face for the contacts. If in several bridges moving in parallel on contact sections, different currents are to be conducted it may, be advisable to provide some of the bridges, in the direction of the contact sections, with grooves laterally embracing the contact banks, thereby selectively providing a larger contact face. However, if exclusively control currents are to be switched, it is adequate for the bridge not to be furnished with grooves and to reduce the bearing face of the contact bridge on the contact bank accordingly.
To improve contact making of the contact bridge, the contact bridge is resiliently guided in an actuating member in a direction vertical to the contacting plane. Due to the flexible abutment of the contact bridge on the contact banks, a safe bearing pressure even in the event of irregularities of the contact bank is ensured. Moreover, an elevated spring pressure can be used for mutually keeping clean the contact faces.
The present invention provides for a reliable guidance of the contact bridge within the actuating lever so that the bridging contact, toward the contact banks, always remains in alignment with the contact sections, preventing deflection from the direction of extension of the contact banks.
Another advantage resides in that the distance covered by the contact bridge toward the contact bank is limited involving special advantages for the assembly of the actuating lever within which the movable contact bridge is safely and rigidly held.
In a preferred embodiment, stops are used as projections on lugs for engaging associated guiding slots within the actuating member. By enabling the contact bridges to engage the actuating lever, easy assembly, movable guidance over the actuating lever and safe arrangement thereover to prevent loss thereof is obtained.
The present invention is suitable for use with slide switches in which the bridging contact performs a straight-forward movement. However, the invention is also suitable for use with contact sections and contact banks, respectively, which are arranged in series at an angle, wherein the contact banks themselves also can be of a curved configuration. It is particularly advantageous for the contact banks to be unidirectionally curved on the contact sections and to be arranged with the same radius of curvature in series. A design of this type is particularly suitable for steering column switches in which the actuating lever performs a swivel movement about a fulcrum resulting in a circular sector-type movement of the bridging contact.
A simple design for the contact banks is disclosed wherein the contact bank can be formed from the contact sections by stamping so that a contact section of that type can also be punched from a simple contact plate.
Another simplification is disclosed in that molded to the contact sections stamped from contact plate are plug connections. Advantageously, the contact sections can be formed from a punching grid. In order to enable the individual contact banks to be more easily placed and held in an injection mold, they are, in addition, connected, during the injection process, to electrically conducting, mechanically connecting bridges that, after the injection operation, are severed by punching, irrespective of whether or not the said severing webs are coated by extrusion with plastic material.
In order to further reduce the bearing face of the contact bridge, the two contact sections serving both for guiding the contact bridge through the ramps and for contact making, in the direction of extension of the contact banks, are spatially separated from one another and are electrically interconnected. The contact areas also can be punched from a single contact plate and can be formed by subsequent deformation, with the two contact areas, advantageously, being electrically interconnected by a web. Suitably, a centering projection can be molded into the said mechanically rigid web with the said centering projection forming a point of attack for the preloading spring. As the contact areas have both a mechanical control function over the associated ramp and a contact-making function over the contact section rigidly connected to the casing, in a preferred embodiment, the contact area includes a curved surface thereby safeguarding that the contact bridge is prevented from interlocking with the ramp. In addition, the slope of the ramp is to be comparatively flat, normally not to exceed 2/10 mm, thereby preventing, in particular, switch noises from occurring and extending the operating life of the switch.